/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.feilong.lib.net.util;

import java.io.UnsupportedEncodingException;
import java.math.BigInteger;

/**
 * Provides Base64 encoding and decoding as defined by RFC 2045.
 *
 * <p>
 * This class implements section <cite>6.8. Base64 Content-Transfer-Encoding</cite> from RFC 2045 <cite>Multipurpose
 * Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</cite> by Freed and Borenstein.
 * </p>
 * <p>
 * The class can be parameterized in the following manner with various constructors:
 * <ul>
 * <li>URL-safe mode: Default off.</li>
 * <li>Line length: Default 76. Line length that aren't multiples of 4 will still essentially end up being multiples of
 * 4 in the encoded data.
 * <li>Line separator: Default is CRLF ("\r\n")</li>
 * </ul>
 * <p>
 * Since this class operates directly on byte streams, and not character streams, it is hard-coded to only encode/decode
 * character encodings which are compatible with the lower 127 ASCII chart (ISO-8859-1, Windows-1252, UTF-8, etc).
 * </p>
 *
 * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>
 * @since 2.2
 * @version $Id$
 */
public class Base64{

    private static final int    DEFAULT_BUFFER_RESIZE_FACTOR = 2;

    private static final int    DEFAULT_BUFFER_SIZE          = 8192;

    /**
     * Chunk size per RFC 2045 section 6.8.
     *
     * <p>
     * The {@value} character limit does not count the trailing CRLF, but counts all other characters, including any
     * equal signs.
     * </p>
     *
     * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
     */
    static final int            CHUNK_SIZE                   = 76;

    /**
     * Chunk separator per RFC 2045 section 2.1.
     *
     * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
     */
    private static final byte[] CHUNK_SEPARATOR              = { '\r', '\n' };

    private static final byte[] EMPTY_BYTE_ARRAY             = new byte[0];

    /**
     * This array is a lookup table that translates 6-bit positive integer index values into their "Base64 Alphabet"
     * equivalents as specified in Table 1 of RFC 2045.
     *
     * Thanks to "commons" project in ws.apache.org for this code.
     * http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     */
    private static final byte[] STANDARD_ENCODE_TABLE        = {
                                                                 'A',
                                                                 'B',
                                                                 'C',
                                                                 'D',
                                                                 'E',
                                                                 'F',
                                                                 'G',
                                                                 'H',
                                                                 'I',
                                                                 'J',
                                                                 'K',
                                                                 'L',
                                                                 'M',
                                                                 'N',
                                                                 'O',
                                                                 'P',
                                                                 'Q',
                                                                 'R',
                                                                 'S',
                                                                 'T',
                                                                 'U',
                                                                 'V',
                                                                 'W',
                                                                 'X',
                                                                 'Y',
                                                                 'Z',
                                                                 'a',
                                                                 'b',
                                                                 'c',
                                                                 'd',
                                                                 'e',
                                                                 'f',
                                                                 'g',
                                                                 'h',
                                                                 'i',
                                                                 'j',
                                                                 'k',
                                                                 'l',
                                                                 'm',
                                                                 'n',
                                                                 'o',
                                                                 'p',
                                                                 'q',
                                                                 'r',
                                                                 's',
                                                                 't',
                                                                 'u',
                                                                 'v',
                                                                 'w',
                                                                 'x',
                                                                 'y',
                                                                 'z',
                                                                 '0',
                                                                 '1',
                                                                 '2',
                                                                 '3',
                                                                 '4',
                                                                 '5',
                                                                 '6',
                                                                 '7',
                                                                 '8',
                                                                 '9',
                                                                 '+',
                                                                 '/' };

    /**
     * This is a copy of the STANDARD_ENCODE_TABLE above, but with + and /
     * changed to - and _ to make the encoded Base64 results more URL-SAFE.
     * This table is only used when the Base64's mode is set to URL-SAFE.
     */
    private static final byte[] URL_SAFE_ENCODE_TABLE        = {
                                                                 'A',
                                                                 'B',
                                                                 'C',
                                                                 'D',
                                                                 'E',
                                                                 'F',
                                                                 'G',
                                                                 'H',
                                                                 'I',
                                                                 'J',
                                                                 'K',
                                                                 'L',
                                                                 'M',
                                                                 'N',
                                                                 'O',
                                                                 'P',
                                                                 'Q',
                                                                 'R',
                                                                 'S',
                                                                 'T',
                                                                 'U',
                                                                 'V',
                                                                 'W',
                                                                 'X',
                                                                 'Y',
                                                                 'Z',
                                                                 'a',
                                                                 'b',
                                                                 'c',
                                                                 'd',
                                                                 'e',
                                                                 'f',
                                                                 'g',
                                                                 'h',
                                                                 'i',
                                                                 'j',
                                                                 'k',
                                                                 'l',
                                                                 'm',
                                                                 'n',
                                                                 'o',
                                                                 'p',
                                                                 'q',
                                                                 'r',
                                                                 's',
                                                                 't',
                                                                 'u',
                                                                 'v',
                                                                 'w',
                                                                 'x',
                                                                 'y',
                                                                 'z',
                                                                 '0',
                                                                 '1',
                                                                 '2',
                                                                 '3',
                                                                 '4',
                                                                 '5',
                                                                 '6',
                                                                 '7',
                                                                 '8',
                                                                 '9',
                                                                 '-',
                                                                 '_' };

    /**
     * Byte used to pad output.
     */
    private static final byte   PAD                          = '=';

    /**
     * This array is a lookup table that translates Unicode characters drawn from the "Base64 Alphabet" (as specified in
     * Table 1 of RFC 2045) into their 6-bit positive integer equivalents. Characters that are not in the Base64
     * alphabet but fall within the bounds of the array are translated to -1.
     *
     * Note: '+' and '-' both decode to 62. '/' and '_' both decode to 63. This means decoder seamlessly handles both
     * URL_SAFE and STANDARD base64. (The encoder, on the other hand, needs to know ahead of time what to emit).
     *
     * Thanks to "commons" project in ws.apache.org for this code.
     * http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     */
    private static final byte[] DECODE_TABLE                 = {
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 62,
                                                                 -1,
                                                                 62,
                                                                 -1,
                                                                 63,
                                                                 52,
                                                                 53,
                                                                 54,
                                                                 55,
                                                                 56,
                                                                 57,
                                                                 58,
                                                                 59,
                                                                 60,
                                                                 61,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 0,
                                                                 1,
                                                                 2,
                                                                 3,
                                                                 4,
                                                                 5,
                                                                 6,
                                                                 7,
                                                                 8,
                                                                 9,
                                                                 10,
                                                                 11,
                                                                 12,
                                                                 13,
                                                                 14,
                                                                 15,
                                                                 16,
                                                                 17,
                                                                 18,
                                                                 19,
                                                                 20,
                                                                 21,
                                                                 22,
                                                                 23,
                                                                 24,
                                                                 25,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 -1,
                                                                 63,
                                                                 -1,
                                                                 26,
                                                                 27,
                                                                 28,
                                                                 29,
                                                                 30,
                                                                 31,
                                                                 32,
                                                                 33,
                                                                 34,
                                                                 35,
                                                                 36,
                                                                 37,
                                                                 38,
                                                                 39,
                                                                 40,
                                                                 41,
                                                                 42,
                                                                 43,
                                                                 44,
                                                                 45,
                                                                 46,
                                                                 47,
                                                                 48,
                                                                 49,
                                                                 50,
                                                                 51 };

    /** Mask used to extract 6 bits, used when encoding */
    private static final int    MASK_6BITS                   = 0x3f;

    /** Mask used to extract 8 bits, used in decoding base64 bytes */
    private static final int    MASK_8BITS                   = 0xff;

    // The static final fields above are used for the original static byte[] methods on Base64.
    // The private member fields below are used with the new streaming approach, which requires
    // some state be preserved between calls of encode() and decode().

    /**
     * Encode table to use: either STANDARD or URL_SAFE. Note: the DECODE_TABLE above remains static because it is able
     * to decode both STANDARD and URL_SAFE streams, but the encodeTable must be a member variable so we can switch
     * between the two modes.
     */
    private final byte[]        encodeTable;

    /**
     * Line length for encoding. Not used when decoding. A value of zero or less implies no chunking of the base64
     * encoded data.
     */
    private final int           lineLength;

    /**
     * Line separator for encoding. Not used when decoding. Only used if lineLength > 0.
     */
    private final byte[]        lineSeparator;

    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * <code>decodeSize = 3 + lineSeparator.length;</code>
     */
    private final int           decodeSize;

    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * <code>encodeSize = 4 + lineSeparator.length;</code>
     */
    private final int           encodeSize;

    /**
     * Buffer for streaming.
     */
    private byte[]              buffer;

    /**
     * Position where next character should be written in the buffer.
     */
    private int                 pos;

    /**
     * Position where next character should be read from the buffer.
     */
    private int                 readPos;

    /**
     * Variable tracks how many characters have been written to the current line. Only used when encoding. We use it to
     * make sure each encoded line never goes beyond lineLength (if lineLength > 0).
     */
    private int                 currentLinePos;

    /**
     * Writes to the buffer only occur after every 3 reads when encoding, an every 4 reads when decoding. This variable
     * helps track that.
     */
    private int                 modulus;

    /**
     * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this Base64 object becomes useless,
     * and must be thrown away.
     */
    private boolean             eof;

    /**
     * Place holder for the 3 bytes we're dealing with for our base64 logic. Bitwise operations store and extract the
     * base64 encoding or decoding from this variable.
     */
    private int                 x;

    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode.
     * <p>
     * When encoding the line length is 76, the line separator is CRLF, and the encoding table is STANDARD_ENCODE_TABLE.
     * </p>
     *
     * <p>
     * When decoding all variants are supported.
     * </p>
     */
    public Base64(){
        this(false);
    }

    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in the given URL-safe mode.
     * <p>
     * When encoding the line length is 76, the line separator is CRLF, and the encoding table is STANDARD_ENCODE_TABLE.
     * </p>
     *
     * <p>
     * When decoding all variants are supported.
     * </p>
     *
     * @param urlSafe
     *            if <code>true</code>, URL-safe encoding is used. In most cases this should be set to
     *            <code>false</code>.
     * @since 1.4
     */
    public Base64(boolean urlSafe){
        this(CHUNK_SIZE, CHUNK_SEPARATOR, urlSafe);
    }

    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode.
     * <p>
     * When encoding the line length is given in the constructor, the line separator is CRLF, and the encoding table is
     * STANDARD_ENCODE_TABLE.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 4 will still essentially end up being multiples of 4 in the encoded data.
     * </p>
     * <p>
     * When decoding all variants are supported.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to nearest multiple of 4).
     *            If {@code lineLength <= 0}, then the output will not be divided into lines (chunks). Ignored when decoding.
     * @since 1.4
     */
    public Base64(int lineLength){
        this(lineLength, CHUNK_SEPARATOR);
    }

    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode.
     * <p>
     * When encoding the line length and line separator are given in the constructor, and the encoding table is
     * STANDARD_ENCODE_TABLE.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 4 will still essentially end up being multiples of 4 in the encoded data.
     * </p>
     * <p>
     * When decoding all variants are supported.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to nearest multiple of 4).
     *            If {@code lineLength <= 0}, then the output will not be divided into lines (chunks). Ignored when decoding.
     * @param lineSeparator
     *            Each line of encoded data will end with this sequence of bytes.
     * @throws IllegalArgumentException
     *             Thrown when the provided lineSeparator included some base64 characters.
     * @since 1.4
     */
    public Base64(int lineLength, byte[] lineSeparator){
        this(lineLength, lineSeparator, false);
    }

    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode.
     * <p>
     * When encoding the line length and line separator are given in the constructor, and the encoding table is
     * STANDARD_ENCODE_TABLE.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 4 will still essentially end up being multiples of 4 in the encoded data.
     * </p>
     * <p>
     * When decoding all variants are supported.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to nearest multiple of 4).
     *            If {@code lineLength <= 0}, then the output will not be divided into lines (chunks). Ignored when decoding.
     * @param lineSeparator
     *            Each line of encoded data will end with this sequence of bytes.
     * @param urlSafe
     *            Instead of emitting '+' and '/' we emit '-' and '_' respectively. urlSafe is only applied to encode
     *            operations. Decoding seamlessly handles both modes.
     * @throws IllegalArgumentException
     *             The provided lineSeparator included some base64 characters. That's not going to work!
     * @since 1.4
     */
    public Base64(int lineLength, byte[] lineSeparator, boolean urlSafe){
        if (lineSeparator == null){
            lineLength = 0; // disable chunk-separating
            lineSeparator = EMPTY_BYTE_ARRAY; // this just gets ignored
        }
        this.lineLength = lineLength > 0 ? (lineLength / 4) * 4 : 0;
        this.lineSeparator = new byte[lineSeparator.length];
        System.arraycopy(lineSeparator, 0, this.lineSeparator, 0, lineSeparator.length);
        if (lineLength > 0){
            this.encodeSize = 4 + lineSeparator.length;
        }else{
            this.encodeSize = 4;
        }
        this.decodeSize = this.encodeSize - 1;
        if (containsBase64Byte(lineSeparator)){
            String sep = newStringUtf8(lineSeparator);
            throw new IllegalArgumentException("lineSeperator must not contain base64 characters: [" + sep + "]");
        }
        this.encodeTable = urlSafe ? URL_SAFE_ENCODE_TABLE : STANDARD_ENCODE_TABLE;
    }

    /**
     * Returns our current encode mode. True if we're URL-SAFE, false otherwise.
     *
     * @return true if we're in URL-SAFE mode, false otherwise.
     * @since 1.4
     */
    public boolean isUrlSafe(){
        return this.encodeTable == URL_SAFE_ENCODE_TABLE;
    }

    /**
     * Returns true if this Base64 object has buffered data for reading.
     *
     * @return true if there is Base64 object still available for reading.
     */
    boolean hasData(){
        return this.buffer != null;
    }

    /**
     * Returns the amount of buffered data available for reading.
     *
     * @return The amount of buffered data available for reading.
     */
    int avail(){
        return buffer != null ? pos - readPos : 0;
    }

    /** Doubles our buffer. */
    private void resizeBuffer(){
        if (buffer == null){
            buffer = new byte[DEFAULT_BUFFER_SIZE];
            pos = 0;
            readPos = 0;
        }else{
            byte[] b = new byte[buffer.length * DEFAULT_BUFFER_RESIZE_FACTOR];
            System.arraycopy(buffer, 0, b, 0, buffer.length);
            buffer = b;
        }
    }

    /**
     * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
     * bytes. Returns how many bytes were actually extracted.
     *
     * @param b
     *            byte[] array to extract the buffered data into.
     * @param bPos
     *            position in byte[] array to start extraction at.
     * @param bAvail
     *            amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
     * @return The number of bytes successfully extracted into the provided byte[] array.
     */
    int readResults(byte[] b,int bPos,int bAvail){
        if (buffer != null){
            int len = Math.min(avail(), bAvail);
            if (buffer != b){
                System.arraycopy(buffer, readPos, b, bPos, len);
                readPos += len;
                if (readPos >= pos){
                    buffer = null;
                }
            }else{
                // Re-using the original consumer's output array is only
                // allowed for one round.
                buffer = null;
            }
            return len;
        }
        return eof ? -1 : 0;
    }

    /**
     * Sets the streaming buffer. This is a small optimization where we try to buffer directly to the consumer's output
     * array for one round (if the consumer calls this method first) instead of starting our own buffer.
     *
     * @param out
     *            byte[] array to buffer directly to.
     * @param outPos
     *            Position to start buffering into.
     * @param outAvail
     *            Amount of bytes available for direct buffering.
     */
    void setInitialBuffer(byte[] out,int outPos,int outAvail){
        // We can re-use consumer's original output array under
        // special circumstances, saving on some System.arraycopy().
        if (out != null && out.length == outAvail){
            buffer = out;
            pos = outPos;
            readPos = outPos;
        }
    }

    /**
     * <p>
     * Encodes all of the provided data, starting at inPos, for inAvail bytes. Must be called at least twice: once with
     * the data to encode, and once with inAvail set to "-1" to alert encoder that EOF has been reached, so flush last
     * remaining bytes (if not multiple of 3).
     * </p>
     * <p>
     * Thanks to "commons" project in ws.apache.org for the bitwise operations, and general approach.
     * http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     * </p>
     *
     * @param in
     *            byte[] array of binary data to base64 encode.
     * @param inPos
     *            Position to start reading data from.
     * @param inAvail
     *            Amount of bytes available from input for encoding.
     */
    void encode(byte[] in,int inPos,int inAvail){
        if (eof){
            return;
        }
        // inAvail < 0 is how we're informed of EOF in the underlying data we're
        // encoding.
        if (inAvail < 0){
            eof = true;
            if (buffer == null || buffer.length - pos < encodeSize){
                resizeBuffer();
            }
            switch (modulus) {
                case 1:
                    buffer[pos++] = encodeTable[(x >> 2) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(x << 4) & MASK_6BITS];
                    // URL-SAFE skips the padding to further reduce size.
                    if (encodeTable == STANDARD_ENCODE_TABLE){
                        buffer[pos++] = PAD;
                        buffer[pos++] = PAD;
                    }
                    break;

                case 2:
                    buffer[pos++] = encodeTable[(x >> 10) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(x >> 4) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(x << 2) & MASK_6BITS];
                    // URL-SAFE skips the padding to further reduce size.
                    if (encodeTable == STANDARD_ENCODE_TABLE){
                        buffer[pos++] = PAD;
                    }
                    break;
                default:
                    break; // other values ignored
            }
            if (lineLength > 0 && pos > 0){
                System.arraycopy(lineSeparator, 0, buffer, pos, lineSeparator.length);
                pos += lineSeparator.length;
            }
        }else{
            for (int i = 0; i < inAvail; i++){
                if (buffer == null || buffer.length - pos < encodeSize){
                    resizeBuffer();
                }
                modulus = (++modulus) % 3;
                int b = in[inPos++];
                if (b < 0){
                    b += 256;
                }
                x = (x << 8) + b;
                if (0 == modulus){
                    buffer[pos++] = encodeTable[(x >> 18) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(x >> 12) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(x >> 6) & MASK_6BITS];
                    buffer[pos++] = encodeTable[x & MASK_6BITS];
                    currentLinePos += 4;
                    if (lineLength > 0 && lineLength <= currentLinePos){
                        System.arraycopy(lineSeparator, 0, buffer, pos, lineSeparator.length);
                        pos += lineSeparator.length;
                        currentLinePos = 0;
                    }
                }
            }
        }
    }

    /**
     * <p>
     * Decodes all of the provided data, starting at inPos, for inAvail bytes. Should be called at least twice: once
     * with the data to decode, and once with inAvail set to "-1" to alert decoder that EOF has been reached. The "-1"
     * call is not necessary when decoding, but it doesn't hurt, either.
     * </p>
     * <p>
     * Ignores all non-base64 characters. This is how chunked (e.g. 76 character) data is handled, since CR and LF are
     * silently ignored, but has implications for other bytes, too. This method subscribes to the garbage-in,
     * garbage-out philosophy: it will not check the provided data for validity.
     * </p>
     * <p>
     * Thanks to "commons" project in ws.apache.org for the bitwise operations, and general approach.
     * http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     * </p>
     *
     * @param in
     *            byte[] array of ascii data to base64 decode.
     * @param inPos
     *            Position to start reading data from.
     * @param inAvail
     *            Amount of bytes available from input for encoding.
     */
    void decode(byte[] in,int inPos,int inAvail){
        if (eof){
            return;
        }
        if (inAvail < 0){
            eof = true;
        }
        for (int i = 0; i < inAvail; i++){
            if (buffer == null || buffer.length - pos < decodeSize){
                resizeBuffer();
            }
            byte b = in[inPos++];
            if (b == PAD){
                // We're done.
                eof = true;
                break;
            }
            if (b >= 0 && b < DECODE_TABLE.length){
                int result = DECODE_TABLE[b];
                if (result >= 0){
                    modulus = (++modulus) % 4;
                    x = (x << 6) + result;
                    if (modulus == 0){
                        buffer[pos++] = (byte) ((x >> 16) & MASK_8BITS);
                        buffer[pos++] = (byte) ((x >> 8) & MASK_8BITS);
                        buffer[pos++] = (byte) (x & MASK_8BITS);
                    }
                }
            }
        }

        // Two forms of EOF as far as base64 decoder is concerned: actual
        // EOF (-1) and first time '=' character is encountered in stream.
        // This approach makes the '=' padding characters completely optional.
        if (eof && modulus != 0){
            x = x << 6;
            switch (modulus) {
                case 2:
                    x = x << 6;
                    buffer[pos++] = (byte) ((x >> 16) & MASK_8BITS);
                    break;
                case 3:
                    buffer[pos++] = (byte) ((x >> 16) & MASK_8BITS);
                    buffer[pos++] = (byte) ((x >> 8) & MASK_8BITS);
                    break;
                default:
                    break; // other values ignored
            }
        }
    }

    /**
     * Returns whether or not the <code>octet</code> is in the base 64 alphabet.
     *
     * @param octet
     *            The value to test
     * @return <code>true</code> if the value is defined in the the base 64 alphabet, <code>false</code> otherwise.
     * @since 1.4
     */
    public static boolean isBase64(byte octet){
        return octet == PAD || (octet >= 0 && octet < DECODE_TABLE.length && DECODE_TABLE[octet] != -1);
    }

    /**
     * Tests a given byte array to see if it contains only valid characters within the Base64 alphabet. Currently the
     * method treats whitespace as valid.
     *
     * @param arrayOctet
     *            byte array to test
     * @return <code>true</code> if all bytes are valid characters in the Base64 alphabet or if the byte array is empty;
     *         false, otherwise
     */
    public static boolean isArrayByteBase64(byte[] arrayOctet){
        for (byte element : arrayOctet){
            if (!isBase64(element) && !isWhiteSpace(element)){
                return false;
            }
        }
        return true;
    }

    /**
     * Tests a given byte array to see if it contains only valid characters within the Base64 alphabet.
     *
     * @param arrayOctet
     *            byte array to test
     * @return <code>true</code> if any byte is a valid character in the Base64 alphabet; false herwise
     */
    private static boolean containsBase64Byte(byte[] arrayOctet){
        for (byte element : arrayOctet){
            if (isBase64(element)){
                return true;
            }
        }
        return false;
    }

    /**
     * Encodes binary data using the base64 algorithm but does not chunk the output.
     *
     * @param binaryData
     *            binary data to encode
     * @return byte[] containing Base64 characters in their UTF-8 representation.
     */
    public static byte[] encodeBase64(byte[] binaryData){
        return encodeBase64(binaryData, false);
    }

    /**
     * Encodes binary data using the base64 algorithm into 76 character blocks separated by CRLF.
     * <p>
     * For a non-chunking version, see {@link #encodeBase64StringUnChunked(byte[])}.
     *
     * @param binaryData
     *            binary data to encode
     * @return String containing Base64 characters.
     * @since 1.4
     */
    public static String encodeBase64String(byte[] binaryData){
        return newStringUtf8(encodeBase64(binaryData, true));
    }

    /**
     * Encodes binary data using the base64 algorithm, without using chunking.
     * <p>
     * For a chunking version, see {@link #encodeBase64String(byte[])}.
     *
     * @param binaryData
     *            binary data to encode
     * @return String containing Base64 characters.
     * @since 3.2
     */
    public static String encodeBase64StringUnChunked(byte[] binaryData){
        return newStringUtf8(encodeBase64(binaryData, false));
    }

    /**
     * Encodes binary data using the base64 algorithm.
     *
     * @param binaryData
     *            binary data to encode
     * @param useChunking
     *            whether to split the output into chunks
     * @return String containing Base64 characters.
     * @since 3.2
     */
    public static String encodeBase64String(byte[] binaryData,boolean useChunking){
        return newStringUtf8(encodeBase64(binaryData, useChunking));
    }

    /**
     * Encodes binary data using a URL-safe variation of the base64 algorithm but does not chunk the output. The
     * url-safe variation emits - and _ instead of + and / characters.
     *
     * @param binaryData
     *            binary data to encode
     * @return byte[] containing Base64 characters in their UTF-8 representation.
     * @since 1.4
     */
    public static byte[] encodeBase64URLSafe(byte[] binaryData){
        return encodeBase64(binaryData, false, true);
    }

    /**
     * Encodes binary data using a URL-safe variation of the base64 algorithm but does not chunk the output. The
     * url-safe variation emits - and _ instead of + and / characters.
     *
     * @param binaryData
     *            binary data to encode
     * @return String containing Base64 characters
     * @since 1.4
     */
    public static String encodeBase64URLSafeString(byte[] binaryData){
        return newStringUtf8(encodeBase64(binaryData, false, true));
    }

    /**
     * Encodes binary data using the base64 algorithm and chunks the encoded output into 76 character blocks
     *
     * @param binaryData
     *            binary data to encode
     * @return Base64 characters chunked in 76 character blocks
     */
    public static byte[] encodeBase64Chunked(byte[] binaryData){
        return encodeBase64(binaryData, true);
    }

    /**
     * Decodes a String containing containing characters in the Base64 alphabet.
     *
     * @param pArray
     *            A String containing Base64 character data
     * @return a byte array containing binary data
     * @since 1.4
     */
    public byte[] decode(String pArray){
        return decode(getBytesUtf8(pArray));
    }

    private static byte[] getBytesUtf8(String pArray){
        try{
            return pArray.getBytes("UTF8");
        }catch (UnsupportedEncodingException e){
            throw new RuntimeException(e);
        }
    }

    /**
     * Decodes a byte[] containing containing characters in the Base64 alphabet.
     *
     * @param pArray
     *            A byte array containing Base64 character data
     * @return a byte array containing binary data
     */
    public byte[] decode(byte[] pArray){
        reset();
        if (pArray == null || pArray.length == 0){
            return pArray;
        }
        long len = (pArray.length * 3) / 4;
        byte[] buf = new byte[(int) len];
        setInitialBuffer(buf, 0, buf.length);
        decode(pArray, 0, pArray.length);
        decode(pArray, 0, -1); // Notify decoder of EOF.

        // Would be nice to just return buf (like we sometimes do in the encode
        // logic), but we have no idea what the line-length was (could even be
        // variable).  So we cannot determine ahead of time exactly how big an
        // array is necessary.  Hence the need to construct a 2nd byte array to
        // hold the final result:

        byte[] result = new byte[pos];
        readResults(result, 0, result.length);
        return result;
    }

    /**
     * Encodes binary data using the base64 algorithm, optionally chunking the output into 76 character blocks.
     *
     * @param binaryData
     *            Array containing binary data to encode.
     * @param isChunked
     *            if <code>true</code> this encoder will chunk the base64 output into 76 character blocks
     * @return Base64-encoded data.
     * @throws IllegalArgumentException
     *             Thrown when the input array needs an output array bigger than {@link Integer#MAX_VALUE}
     */
    public static byte[] encodeBase64(byte[] binaryData,boolean isChunked){
        return encodeBase64(binaryData, isChunked, false);
    }

    /**
     * Encodes binary data using the base64 algorithm, optionally chunking the output into 76 character blocks.
     *
     * @param binaryData
     *            Array containing binary data to encode.
     * @param isChunked
     *            if <code>true</code> this encoder will chunk the base64 output into 76 character blocks
     * @param urlSafe
     *            if <code>true</code> this encoder will emit - and _ instead of the usual + and / characters.
     * @return Base64-encoded data.
     * @throws IllegalArgumentException
     *             Thrown when the input array needs an output array bigger than {@link Integer#MAX_VALUE}
     * @since 1.4
     */
    public static byte[] encodeBase64(byte[] binaryData,boolean isChunked,boolean urlSafe){
        return encodeBase64(binaryData, isChunked, urlSafe, Integer.MAX_VALUE);
    }

    /**
     * Encodes binary data using the base64 algorithm, optionally chunking the output into 76 character blocks.
     *
     * @param binaryData
     *            Array containing binary data to encode.
     * @param isChunked
     *            if <code>true</code> this encoder will chunk the base64 output into 76 character blocks
     * @param urlSafe
     *            if <code>true</code> this encoder will emit - and _ instead of the usual + and / characters.
     * @param maxResultSize
     *            The maximum result size to accept.
     * @return Base64-encoded data.
     * @throws IllegalArgumentException
     *             Thrown when the input array needs an output array bigger than maxResultSize
     * @since 1.4
     */
    public static byte[] encodeBase64(byte[] binaryData,boolean isChunked,boolean urlSafe,int maxResultSize){
        if (binaryData == null || binaryData.length == 0){
            return binaryData;
        }

        long len = getEncodeLength(binaryData, isChunked ? CHUNK_SIZE : 0, isChunked ? CHUNK_SEPARATOR : EMPTY_BYTE_ARRAY);
        if (len > maxResultSize){
            throw new IllegalArgumentException(
                            "Input array too big, the output array would be bigger (" + len + ") than the specified maxium size of "
                                            + maxResultSize);
        }

        Base64 b64 = isChunked ? new Base64(urlSafe) : new Base64(0, CHUNK_SEPARATOR, urlSafe);
        return b64.encode(binaryData);
    }

    /**
     * Decodes a Base64 String into octets
     *
     * @param base64String
     *            String containing Base64 data
     * @return Array containing decoded data.
     * @since 1.4
     */
    public static byte[] decodeBase64(String base64String){
        return new Base64().decode(base64String);
    }

    /**
     * Decodes Base64 data into octets
     *
     * @param base64Data
     *            Byte array containing Base64 data
     * @return Array containing decoded data.
     */
    public static byte[] decodeBase64(byte[] base64Data){
        return new Base64().decode(base64Data);
    }

    /**
     * Checks if a byte value is whitespace or not.
     *
     * @param byteToCheck
     *            the byte to check
     * @return true if byte is whitespace, false otherwise
     */
    private static boolean isWhiteSpace(byte byteToCheck){
        switch (byteToCheck) {
            case ' ':
            case '\n':
            case '\r':
            case '\t':
                return true;
            default:
                return false;
        }
    }

    /**
     * Encodes a byte[] containing binary data, into a String containing characters in the Base64 alphabet.
     *
     * @param pArray
     *            a byte array containing binary data
     * @return A String containing only Base64 character data
     * @since 1.4
     */
    public String encodeToString(byte[] pArray){
        return newStringUtf8(encode(pArray));
    }

    private static String newStringUtf8(byte[] encode){
        String str = null;
        try{
            str = new String(encode, "UTF8");
        }catch (UnsupportedEncodingException ue){
            throw new RuntimeException(ue);
        }
        return str;
    }

    /**
     * Encodes a byte[] containing binary data, into a byte[] containing characters in the Base64 alphabet.
     *
     * @param pArray
     *            a byte array containing binary data
     * @return A byte array containing only Base64 character data
     */
    public byte[] encode(byte[] pArray){
        reset();
        if (pArray == null || pArray.length == 0){
            return pArray;
        }
        long len = getEncodeLength(pArray, lineLength, lineSeparator);
        byte[] buf = new byte[(int) len];
        setInitialBuffer(buf, 0, buf.length);
        encode(pArray, 0, pArray.length);
        encode(pArray, 0, -1); // Notify encoder of EOF.
        // Encoder might have resized, even though it was unnecessary.
        if (buffer != buf){
            readResults(buf, 0, buf.length);
        }
        // In URL-SAFE mode we skip the padding characters, so sometimes our
        // final length is a bit smaller.
        if (isUrlSafe() && pos < buf.length){
            byte[] smallerBuf = new byte[pos];
            System.arraycopy(buf, 0, smallerBuf, 0, pos);
            buf = smallerBuf;
        }
        return buf;
    }

    /**
     * Pre-calculates the amount of space needed to base64-encode the supplied array.
     *
     * @param pArray
     *            byte[] array which will later be encoded
     * @param chunkSize
     *            line-length of the output (<= 0 means no chunking) between each
     *            chunkSeparator (e.g. CRLF).
     * @param chunkSeparator
     *            the sequence of bytes used to separate chunks of output (e.g. CRLF).
     *
     * @return amount of space needed to encoded the supplied array. Returns
     *         a long since a max-len array will require Integer.MAX_VALUE + 33%.
     */
    private static long getEncodeLength(byte[] pArray,int chunkSize,byte[] chunkSeparator){
        // base64 always encodes to multiples of 4.
        chunkSize = (chunkSize / 4) * 4;

        long len = (pArray.length * 4) / 3;
        long mod = len % 4;
        if (mod != 0){
            len += 4 - mod;
        }
        if (chunkSize > 0){
            boolean lenChunksPerfectly = len % chunkSize == 0;
            len += (len / chunkSize) * chunkSeparator.length;
            if (!lenChunksPerfectly){
                len += chunkSeparator.length;
            }
        }
        return len;
    }

    // Implementation of integer encoding used for crypto
    /**
     * Decodes a byte64-encoded integer according to crypto standards such as W3C's XML-Signature
     *
     * @param pArray
     *            a byte array containing base64 character data
     * @return A BigInteger
     * @since 1.4
     */
    public static BigInteger decodeInteger(byte[] pArray){
        return new BigInteger(1, decodeBase64(pArray));
    }

    /**
     * Encodes to a byte64-encoded integer according to crypto standards such as W3C's XML-Signature
     *
     * @param bigInt
     *            a BigInteger
     * @return A byte array containing base64 character data
     * @throws NullPointerException
     *             if null is passed in
     * @since 1.4
     */
    public static byte[] encodeInteger(BigInteger bigInt){
        if (bigInt == null){
            throw new NullPointerException("encodeInteger called with null parameter");
        }
        return encodeBase64(toIntegerBytes(bigInt), false);
    }

    /**
     * Returns a byte-array representation of a <code>BigInteger</code> without sign bit.
     *
     * @param bigInt
     *            <code>BigInteger</code> to be converted
     * @return a byte array representation of the BigInteger parameter
     */
    static byte[] toIntegerBytes(BigInteger bigInt){
        int bitlen = bigInt.bitLength();
        // round bitlen
        bitlen = ((bitlen + 7) >> 3) << 3;
        byte[] bigBytes = bigInt.toByteArray();

        if (((bigInt.bitLength() % 8) != 0) && (((bigInt.bitLength() / 8) + 1) == (bitlen / 8))){
            return bigBytes;
        }
        // set up params for copying everything but sign bit
        int startSrc = 0;
        int len = bigBytes.length;

        // if bigInt is exactly byte-aligned, just skip signbit in copy
        if ((bigInt.bitLength() % 8) == 0){
            startSrc = 1;
            len--;
        }
        int startDst = bitlen / 8 - len; // to pad w/ nulls as per spec
        byte[] resizedBytes = new byte[bitlen / 8];
        System.arraycopy(bigBytes, startSrc, resizedBytes, startDst, len);
        return resizedBytes;
    }

    /**
     * Resets this Base64 object to its initial newly constructed state.
     */
    private void reset(){
        buffer = null;
        pos = 0;
        readPos = 0;
        currentLinePos = 0;
        modulus = 0;
        eof = false;
    }

    // Getters for use in testing

    int getLineLength(){
        return lineLength;
    }

    byte[] getLineSeparator(){
        return lineSeparator.clone();
    }
}
